Following steps have been disclosed as a conventional method for the processing of a silicon wafer (see, for example, Nonpatent literature 1).
A single silicon crystal rod pulled up from a crucible is cut at its frond and rear ends, and then divided into a number of blocks. The block has its periphery abraded until it has a diameter close to a desired one. Then, an orientation flat or a notch is formed to mark a specified orientation of the crystal. The single crystal ingot thus formed is first sliced at a specified angle to the longitudinal axis of the ingot with the blade of a cutter into thin, disc-like slices, thereby producing a plurality of silicon wafers as shown in FIG. 2(a) (step 1). FIG. 2(b) shows the cross-sections of silicon wafers having undergone the corresponding steps of FIG. 2(a).
The silicon wafer thus obtained is subjected to cleaning using, for example, an alkaline detergent in order to remove oils adhered possibly as a result of processing such as peripheral abrasion, slicing step 1, etc. (step 2)
Then, wafers are automatically transported to and from, for example, by a robot while they are subjected to machining processes and are processed into devices. The peripheral edge of a wafer is beveled because a wafer whose peripheral edge is not beveled and thus is rectangular will tend to develop notches and flaws, and silicon particles as a result of mechanical impacts to the wafer encountered by accident during transportation might degrade the surface of adjacent wafers. To prevent the development of such notches and flaws, the peripheral edge of a silicon wafer is beveled with a diamond grinder (step 3). The beveling performed during step 3 is also effective for preventing the occurrence of an abnormal development (crown phenomenon) of a film along the periphery of a wafer during the epitaxial growth of a film in a subsequent step or during the application of a photo resist. A wafer having undergone step 3 or beveling step is subjected to alkaline cleaning (step 4). During step 4, contaminants that might occur as a result of beveling during step 3 are removed.
Then, degraded superficial layers developed on the surfaces of a wafer which would occur as a result of slicing performed during step 1 are removed by lapping so that the smoothness of the surfaces of the wafer and their parallelism can be improved (step 5). After the lapping step 5, the wafer is subjected to alkaline cleaning (step 6). During step 6, contaminants that might occur as a result of lapping during step 5 are removed.
Then, the wafer having undergone the lapping step 5 is subjected to fine beveling (step 7). The wafer having undergone the fine beveling step 7 is subjected to alkaline cleaning (step 8). During step 8, contaminants that might occur as a result of fine beveling during step 7 are removed.
Subsequently, the wafer is etched by being immersed in an acidic etching solution (step 9). During step 9, any degraded superficial layers that might occur on the front and rear surfaces of the wafer as a result of the above machining are completely eliminated.
Wafers processed as described above will undergo additional processing (not illustrated) such as abrasion, heating, mirror polishing, cleaning, etc. to receive further processing necessary for the fabrication of devices.
Nonpatent literature 1: Shimura, F., “Engineering of Semiconductor Silicon Crystals,” Maruzen, Sep. 30, 1993, p. 104.